BEIJING -- China's rapidly expanding but overtaxed aviation system yesterday saw its fifth air disaster in four months and the worst ever in Chinese history.

All 133 passengers and eight crew members were killed when a Boeing 737-300 jetliner slammed into a mountain near the southern China tourist center of Guilin at 7:54 a.m. yesterday in what was believed to be clear weather.

China's official news agency reported late last night that among the passengers on the flight from Canton were nine Taiwanese, two Spaniards, one Canadian and one traveler from Macao. The rest of the passengers are believed to have been mainland Chinese.

Witnesses said the jet belched smoke before it hit a mountain and exploded into fragments, the state news agency reported.

Western aviation sources here and Chinese officials in Guilin said that debris from the crash are scattered widely over mountains about 15 miles from Guilin.

The Guilin area is famous for its sharply rising limestone peaks, scenery that draws hundreds of thousands of tourists each year but that also enlivens even normal landings at its airport. One unofficial report last night indicated that the pilot was warned by Guilin air traffic controllers that he was descending too fast.

The disaster is the worst in Chinese history, surpassing the death toll of 128 when a hijacked passenger jet crashed into two parked planes at the Canton airport in 1990.

Luo Gan, secretary general of China's State Council, who flew to the crash site yesterday, said that China would make "the utmost effort" to investigate the cause, the official news agency later said.

In Seattle, a Boeing Co. official identified the crashed plane as a 737-300 jet, which was delivered in May 1991 and which has had a record since then of relatively few flight hours and landings.

It was owned by China Southern Airlines, one of several regional state carriers that have sprung up here in recent years with the decentralization of China's airline industry.

These carriers have been struggling to keep up with the rapidly growing demands being put on China's aviation system. With China's economy booming and foreign interest in traveling here rebounding to a record level, the Chinese airline industry has been growing at an annual rate of 28 percent this year, the Civil Aviation Authority of China recently reported. This has resulted in swamped airport facilities and a shortage of qualified personnel.

Yesterday's air crash was China's fifth since July. The others all involved aircraft built in the former Soviet Union:

* A helicopter dropping leaflets advertising cosmetics crashed into a building, exploded and landed on a crowd November 8 in the central city of Zhengzhou, killing 33 people.

* A chartered plane crashed into a mountain while taking off in northwestern Gansu Province October 9, killing nine French tourists and five crew members.

* A helicopter crashed near the Great Wall outside Beijing August 11, killing 15, including 11 Japanese.